The salts of formula I are known as active ingredients of pesticides and their preparation and properties have been described in the literature. The mono-ammonium salts of formula I, however, are never described as appearing in a form other than as hygroscopic products, which are not resistant against the humidity of the normal atmosphere so that their application as pesticides was therefore only brought about by dissolving the products in water and selling the product in aqueous solutions.
The inconvenience of this procedure is clear. It was therefore the aim of our invention to find a method whereby the mon-ammonium salts of formula I--especially the mono-isopropylammonium salt of N-(phosphonomethyl)-glycine and the mono-isopropylammonium salt of (3-amino-3-carboxypropyl)-methane phosphonic acid can be obtained in a form which is non-hygroscopic, enabling thus the transportation, commercialization and even the use in solid form, or--when direct use of the pesticide on the field is carried out in aqueous solution--to ensure that the solid can be dissolved before use, bringing thus transportation and storage to reasonable costs as compared with the present situation when aqueous solutions are transported and stored. The aqueous solutions in commerce contain 30-50% of the active ingredient as a maximum. Handling of the hygroscopic salts also causes environmental and health-care problems which would be avoided with non-sticky, non-hygroscopic products. The products have mostly acidic character and attack even the material in which they are transported so that greatest care and the proper material for their protection is needed--which all increase the costs of application.
The most important representatives of the compounds of formula I are the pesticide ingredients mono-isopropylammonium salt of N-(phosphonomethyl)-glycine and the mono-isopropylammonium salt of (3-amino-3-carboxypropyl)-methane phosphinic acid--however their ammonium-salts are also important.
The above salts, their preparation and use are described in several publications such as U.S. Pat. Nos. 3,315,675, 3,56,672, 4,405,531, 3,868,407, 4,140,513, 4,315,765, 4,397,676 and HU-Patent 184,601 as well as U.S. Pat. Nos. 3,288,846, 4,507,250, 4,147,719, 4,487,724, German Patent 3,312,165, European Patents 249,188, 265,412, 301,391, and Japanese Patents 60/248,190, 02/190,196, 59/181,288.
Different methods were developed to avoid the consequences mentioned above. Thus different additives were proposed as auxiliary agents to ensure the production of wettable powders and their use e.g. European Patents 256,942, 352,508, Japanese Patents 01,42,409, 58,18,311, 62/175,407, 62/175,408, and U.S. Pat. No. 4,405,531. However when used in practice, great care has to be taken to protect these powders against humidity, to use up the bags when opened, to store the products under proper conditions etc.--otherwise the additional materials do not give the results that are desired when used over a long time period. Another approach to the problem was the suggestion to spray-dry the product (Jap. Pat. 63 10. 701) or again a different one to admix the salt with a solvent and a moulded surface active agent--giving thus a mixture from which the solvent is evaporated and the surface active agent is cooled until solidified, whereupon the solid product is formulated (European Patent 02,06,537).
The preparation of the salts is mostly brought about by reacting the acidic partner with the basic partner reactant in aqueous media, (e.g. Hungarian Patent 185,003, Swiss Patent 620,812 and German Patent 2,717,440) though the literature also teaches reaction of the acid with the basic reactant without solvents, whereupon the mould of surface active agent is added to the reaction mixture and formulation is carried out after cooling of the mixture. (See also Spanish Patent 530,743 where benzene or water are proposed as solvents for a similar method.)
All publications are common--when making any statement about the quality of the products obtained--that they are hygroscopic e.g. German Patent No.2,717,440; Swiss Patent No.620,812 for the ammonium salt of glufosinate, and some state that the products are solidified as glassy materials which can be ground in mortars but still are hygroscopic when stored.
According to Hung. Pat. Appl. 1322/90 a new formulation of N-(phosphonomethyl)-glycine is disclosed consisting of a water-soluble bag containing the sodium or the potassium salt of N-(phosphonomethyl)-glycine as a wettable powder, which is easy to use. The authors of said patent teach, that they were unable to make similar formulations using the mono-isopropylammonium salt of N-(phosphonomethyl)-glycine because of the extreme hygroscopic nature of the mono-isopropylammonium salt. Nor is the aqueous solution of the mono-isopropylammonium salt of N-(phosphonomethyl)-glycine suitable (according to said publication) because the solution dissolves the material of the bag before use.
When investigating some of the products obtained according to some of the known methods e.g. when reproducing the processes of European patent 02/56,608 and Spanish Patent 530,743 we found that these mono-isopropylammonium salts always contained certain amounts of di-ammonium-salts of formula V together with acids of formula II ##STR5##
The presence of small amounts of the di-ammonium-salts of the formula V is not evident from the analysis data of the products obtained by way of classical analysis methods: the content of free acids of formula II together with the content of di-ammonium-salts of formula V might give analytical data as a total result which hide the presence of the di-ammonium salts in the products.
When isolating di-ammonium-salts of formula V we ascertained that these salts differ considerably from the mono-ammonium salts as regards hygroscopicity so that slight amounts of the di-ammonium-salts influence the hygroscopic properties of such salts dramatically.
When investigating the N-(phosphonomethyl)-glycine obtained with known methods by means of FT-IR spectroscopy we found that the products always contained the carbonyl valency oscillation bonds of free N-(phosphonomethyl)-glycine at 1717 and 1733 cm.sup.-1 wave length and the carboxylate oscillations of the free carboxylate in the N-phosphonomethyl)-glycine di-isopropyl-ammonium-salt at 1561 and 1633 cm.sup.-1. The change of the proportions of these bonds shows the change in the ratio of components. This was shown by preparing standard samples of the mono- and the di-iso-propyl-ammonium salts and taking their calibration spectra.
It can be seen from the IR spectroscopic data that also glufosinate exists in two different forms of twin-ionic structure. Thus the carboxyl group can appear both in dissociated form at 1640 and 1600 cm.sup.-1 and in non-dissociated form at the absorption band at 1733 cm.sup.-1 and 1728.
Care has to be taken when preparing the samples as well, Sometimes the mono-ammonium-salts--which are contaminated with di-ammonium-salts as well as with the free acid--are subject to additional reaction steps when the samples are dissolved before taking the spectra--giving thus results that are not typical for the product before measurement.
When comparing the spectra obtained with our own methods it is clear that in the products prepared according to our invention the un-dissociated carboxyl group absorption bonds disappear at 1730 cm.sup.-1 and the dissociated carboxyl bonds which are characteristic for the salts increase at 1640 and 1600 cm.sup.-1.
If one already has the above spectroscopic data the HPLC methods and automatic melting point analytical methods can then be used to complete the definition of the properties of the new salts.
"Non-hygroscopic" according to our invention means, that when exposed at 25.degree. C. to an environment containing 60% humidity no observable uptake of water takes place within 3 weeks or this uptake is less than 0.1%. The salts are crystalline, they have melting point ranges that are different from those published before and their water-solubility is somewhat increased as compared with the salts prepared with the known methods.